Projection display device and back projection display device using the display device

ABSTRACT

A projection display apparatus includes a light source ( 1 ), an illumination system ( 8 ), a reflection system ( 9 ), a reflection-type light modulator ( 10 ), a lens element ( 11 ), and a projection system ( 12 ). The optical axis ( 8   a ) of the illumination system ( 8 ) and the optical axis ( 12   a ) of the projection system ( 12 ) are skew lines. The lens element ( 11 ) allows the exit pupil ( 8   b ) of the illumination system ( 8 ) to be conjugated substantially with the entrance pupil ( 12   b ) of the projection system ( 12 ). Thus, the reflection-type light modulator ( 10 ) and the projection system ( 12 ) can be arranged coaxially. Moreover, mechanical contact or interference between the optical components can be eliminated, and the space can be utilized efficiently. This configuration can provide an inexpensive compact projection display apparatus using a reflection-type light modulator.

TECHNICAL FIELD

[0001] The present invention relates to a projection display apparatusthat can project a large-screen image onto a screen by using areflection-type spatial light modulator, and a rear-projection displayapparatus.

BACKGROUND ART

[0002] Projection display apparatuses using various types of spatiallight modulators conventionally are known as large-screen imageequipment. Recently, a reflection-type spatial light modulator with highdisplay efficiency such as DMD (digital micro-mirror device) has beenreceiving attention (e.g., JP 2000-98272 A).

[0003]FIGS. 16A and 16B show the configuration of a projection displayapparatus using a DMD as a spatial light modulator. FIG. 16A is a topview of the apparatus, and FIG. 16B is a side view thereof. Thisprojection display apparatus includes the following: a lamp 161 foremitting white light; an elliptical mirror 162 for condensing theemitted light of the lamp 161; a rotating color filter 164 that islocated in the vicinity of a long focus of the elliptical mirror 162 andselectively transmits three primary colors (red, green, and blue) oflight in sequence; a focusing lens 165; a plane mirror 166; a DMD 167for modulating incident light to form an optical image; and a projectionlens 168 for magnifying and projecting the optical image formed on theDMD 167 onto a screen (not shown).

[0004] As the lamp 161, e.g., a super-high pressure mercury lamp orxenon lamp may be used. These lamps provide high brightness with arelatively small light-emitting portion, so that the emitted light canbe condensed efficiently. The focusing lens 165 suppresses thedivergence of light that has passed through the rotating color filter164 and directs the light toward the DMD 167 and the projection lens168.

[0005]FIG. 17A is a schematic front view of the DMD 167. FIG. 17B is aschematic side view showing the principle of operation of small mirrors171 on the DMD 167. As shown in FIG. 17A, the DMD 167 includes atwo-dimensional array of small mirrors 171 that are provided for eachpixel. The inclination of the individual small mirrors 171 is controlledby the electrostatic effect of memory devices located directly under thesmall mirrors 171 so that a reflection angle of the incident light ischanged for each pixel, thereby producing the ON/OFF states.

[0006]FIG. 17B illustrates a condition in which a small mirror 171 isinclined at ±10 degrees with respect to the plane of the DMD 167. Forincident light 172 that tilts 20 degrees from a normal to the plane ofthe DMD 167, when the small mirror 171 is in the ON (+10 degrees) state,reflected light 173 enters the projection lens 168, and a pixel isdisplayed on the screen. When the small mirror is in the OFF (−10degrees) state, reflected light 174 does not enter the projection lens168, and a pixel is not displayed on the screen. It is possible toexpress the gray scale by temporally controlling the ON/OFF switching ofeach pixel.

[0007] Each of the mirrors 171 on the DMD 167 is rotated in a plane thatforms an angle of 45 degrees with a minor axis 176 of the display area(this angle is referred to as “bearing angle” in the following), asshown in FIG. 17A.

[0008] To ensure appropriate operation of the DMD 167 and to avoidmechanical contact or interference between the optical components suchas the focusing lens 165 and the projection lens 168, the plane mirror166 is arranged so that the optical path of light emanating from thefocusing lens 165 bends three-dimensionally and the light enters the DMD167 at a predetermined incident angle, as shown in FIGS. 16A and 16B.

[0009] A central axis (a normal passing through the center of aneffective portion in the DMD 167) 167 a of the DMD 167 does not coincidewith an optical axis 168 a of the projection lens 168, but is offset(shifted) from the optical axis 168 a. Therefore, the projection lens168 uses only part of the field angle of an image circle for projectingan optical image formed on the DMD 167.

[0010] However, the projection display apparatus as shown in FIGS. 16Aand 16B has the following problems.

[0011] First, the central axis 167 a of the DMD 167 is offset from theoptical axis 168 a of the projection lens 168, so that excess space isnecessary in the height direction, making it difficult to reduce thesize of the whole apparatus.

[0012] Second, when this apparatus is used in a rear-projection displayapparatus, the optical axis 168 a of the projection lens 168 is offsetfrom the central axis of a projected image. Therefore, the central axis(a normal passing through the center of an effective portion of ascreen) of a transmission-type screen that is held by a cabinet alsoshould be offset from the optical axis 168 a of the projection lens 168.Accordingly, the field angle increases in proportion to the amount ofoffset, which in turn increases not only the size of the projection lens168, but also the angle of incidence of light on a Fresnel lens of thescreen. Thus, flare or stray light is increased on the periphery of thescreen, and the display images have poor quality.

[0013] Moreover, the field angles with respect to the most peripheralportions (four corners) of the screen differ from one another, resultingin nonuniform resolution or brightness on the screen.

[0014] Therefore, a projection system using right projection(non-offset) is suitable for the rear-projection display apparatus.

[0015] In contrast, a configuration that can achieve right projection byusing a DMD has been proposed (e.g., JP 2001-166118 A).

[0016] According to this configuration, a TIR (total internalreflection) prism consisting of two or three pieces of prism is arrangedbetween a projection lens and a DMD. Then, total reflection generatedbetween the air gaps of each piece of prism is utilized to achieve rightprojection.

[0017] However, one side of a projected image can be blurred if there isnonuniformity in the air gaps of the TIR prism, so that extremely strictaccuracy is required. Moreover, the TIR prism is a very expensivecomponent and thus increases the cost of the whole apparatus.

DISCLOSURE OF INVENTION

[0018] Therefore, with the foregoing in mind, it is an object of thepresent invention to provide a small inexpensive projection displayapparatus that can achieve high-uniformity display images and rightprojection by using a reflection-type light modulator such as DMD, and arear-projection display apparatus using the projection displayapparatus.

[0019] A projection display apparatus of the present invention includesthe following: a light source; an illumination system for condensinglight emitted from the light source into illumination light; areflection system for bending an optical path of the illumination light;a reflection-type light modulator that is illuminated with theillumination light bent by the reflection system and forms an opticalimage in accordance with an image signal; a projection system forprojecting the optical image formed on the reflection-type lightmodulator; and a lens element arranged on optical paths of incidentlight and exit light of the reflection-type light modulator. The opticalaxis of the illumination system and the optical axis of the projectionsystem are skew lines. The lens element allows the exit pupil of theillumination system to be conjugated substantially with the entrancepupil of the projection system.

[0020] A rear-projection display apparatus of the present inventionincludes the projection display apparatus of the present invention, atransmission-type screen for displaying an image projected by theprojection display apparatus, and a cabinet for housing the projectiondisplay apparatus and holding the transmission-type screen.

BRIEF DESCRIPTION OF DRAWINGS

[0021]FIG. 1 is an x-z plan view showing the configuration of aprojection display apparatus according to Embodiment 1 of the presentinvention.

[0022]FIG. 2 is an x-y plan view showing the configuration of aprojection display apparatus according to Embodiment 1 of the presentinvention.

[0023]FIG. 3 is a y-z plan view showing the configuration of aprojection display apparatus according to Embodiment 1 of the presentinvention.

[0024]FIG. 4A is a front view of a first lens array in a projectiondisplay apparatus according to Embodiment 1 of the present invention,and FIG. 4B is a side view of the first lens array.

[0025]FIG. 5A is a front view of a second lens array in a projectiondisplay apparatus according to Embodiment 1 of the present invention,and FIG. 5B is a side view of the second lens array.

[0026]FIG. 6 is an x-z plan view showing the configuration of aprojection display apparatus according to Embodiment 2 of the presentinvention.

[0027]FIG. 7 is a y-z plan view showing the configuration of aprojection display apparatus according to Embodiment 2 of the presentinvention.

[0028]FIG. 8A is an x-z plan view showing the configuration of aprojection display apparatus according to Embodiment 3 of the presentinvention.

[0029]FIG. 8B is a front view of a DMD when viewed from the direction ofthe arrow on the line 8B-8B in FIG. 8A.

[0030]FIG. 9 is a y-z plan view showing the configuration of aprojection display apparatus according to Embodiment 3 of the presentinvention.

[0031]FIG. 10A is a schematic diagram for illustrating the position andshape of an entrance pupil of a projection lens in a projection displayapparatus according to Embodiment 2 of the present invention.

[0032]FIG. 10B is a schematic diagram for illustrating the position andshape of an entrance pupil of a projection lens in a projection displayapparatus according to Embodiment 3 of the present invention.

[0033]FIG. 11A is a front view of a first lens array in a projectiondisplay apparatus according to Embodiment 3 of the present invention,and FIG. 11B is a cross-sectional view taken along the line 11B-11B inFIG. 11A.

[0034]FIG. 12A is a front view of a second lens array in a projectiondisplay apparatus according to Embodiment 3 of the present invention,and FIG. 12B is a cross-sectional view taken along the line 12B-12B inFIG. 12A.

[0035]FIG. 13 is an x-z plan view showing the configuration of aprojection display apparatus according to Embodiment 4 of the presentinvention.

[0036]FIG. 14A is a perspective front view of a rear-projection displayapparatus according to Embodiment 5 of the present invention, and FIG.14B is a perspective side view of the apparatus.

[0037]FIG. 15 is a perspective view of a rear-projection displayapparatus according to Embodiment 6 of the present invention.

[0038]FIG. 16A is a top view showing the configuration of a conventionalprojection display apparatus that uses a DMD as a spatial lightmodulator, and FIG. 16B is a side view of the apparatus.

[0039]FIG. 17A is a schematic front view of a DMD, and FIG. 17B is aschematic side view for illustrating the principle of operation of theDMD.

BEST MODE FOR CARRYING OUT THE INVENTION

[0040] In a projection display apparatus of the present invention, theoptical axis of the illumination system and the optical axis of theprojection system are skew lines, and the lens element allows the exitpupil of the illumination system to be conjugated substantially with theentrance pupil of the projection system. Thus, the projection displayapparatus can achieve a small size, low cost, and right projection byusing a reflection-type light modulator.

[0041] In the present invention, the geometric relationship between theoptical axis of the illumination system and the optical axis of theprojection system is expressed by skew lines, which means that the twooptical axes do not lie in the same plane, i.e., the two optical axesare not parallel while they do not intersect.

[0042] In the projection display apparatus of the present invention, itis preferable that the entrance pupil is eccentric with respect to theoptical axis of the projection system.

[0043] In this case, it is preferable that a converging angle in theeccentric direction of the projection system is smaller than aconverging angle in the direction perpendicular to the eccentricdirection.

[0044] It is preferable that the projection system includes a focusadjusting mechanism that does not rotate around the optical axis of theprojection system.

[0045] In the projection display apparatus of the present invention, itis preferable that when viewed from the direction perpendicular to boththe optical axis of the illumination system and the optical axis of theprojection system, an apparent point of intersection of the optical axisof the illumination system and the optical axis of the projection systemis located between the lens element and the projection system.

[0046] It is preferable that the optical axis of the reflection-typelight modulator coincides with the optical axis of the projectionsystem.

[0047] It is preferable that the projection display apparatus of thepresent invention further includes a first cabinet and a second cabinet.The first cabinet may hold the illumination system and include an exitwindow through which light emanating from the illumination systempasses. The second cabinet may hold the reflection system, thereflection-type light modulator, the lens element, and the projectionsystem and include an entrance window through which light from theillumination system enters. The exit window and the entrance window maybe coupled together.

[0048] In this case, it is preferable that a coupling member is providedbetween the exit window and the entrance window, and the coupling memberincludes an adjusting mechanism for adjusting an optical axis or opticalpath length.

[0049] In the projection display apparatus of the present invention, theillumination system preferably includes an optical integrator element.

[0050] In this case, it is preferable that the optical integratorelement includes two lens array plates, and each of a plurality oflenses that constitute at least the lens array plate located closer tothe light source is decentered appropriately.

[0051] Next, a first rear-projection display apparatus of the presentinvention includes the projection display apparatus of the presentinvention, a transmission-type screen for displaying an image projectedby the projection display apparatus, and a cabinet for housing theprojection display apparatus and holding the transmission-type screen.This rear-projection display apparatus can display images with highquality and high uniformity in brightness or resolution.

[0052] A second rear-projection display apparatus of the presentinvention includes a plurality of projection display apparatuses of thepresent invention, transmission-type screens for displaying imagesprojected by the projection display apparatuses, and a cabinet forhousing the projection display apparatuses and holding thetransmission-type screens. This rear-projection display apparatus canperform multi-screen display with high image quality and a smalldifference in image quality between the screens.

[0053] It is preferable that the first and second projection displayapparatuses include a field stop on the transmission-type screen side.

[0054] Hereinafter, specific embodiments of a projection displayapparatus and a rear-projection display apparatus of the presentinvention will be described with reference to the drawings.

[0055] Embodiment 1

[0056]FIG. 1 shows the configuration of a projection display apparatusof Embodiment 1 of the present invention. Reference numeral 1 denotes alamp as a light source, 8 denotes an illumination system, 9 denotes areflection mirror as a reflection system, 10 denotes a DMD as areflection-type light modulator, 11 denotes a planoconvex lens as a lenselement, and 12 denotes a projection lens as a projection system.

[0057] When an xyz rectangular coordinate system is defined as shown inthe drawings, FIG. 1 illustrates the configuration taken along the x-zplane. Similarly, FIGS. 2 and 3 illustrate the configurations takenalong the x-y plane and the y-z plane, respectively.

[0058] An elliptical mirror 2 condenses emitted light of the lamp 1 andforms a focusing spot in the vicinity of the long focus. A UV-IR cutfilter 3 removes ultraviolet and infrared light components from theemitted light of the lamp 1.

[0059] The illumination system 8 includes a rotating color filter 4, acondenser lens 5, a first lens array 6, and a second lens array 7.

[0060] The rotating color filter 4 is formed by combining three primarycolor filters into a disk. The rotating color filter 4 is located in thevicinity of the focusing spot and is rotated so as to selectivelytransmit red, green, and blue colors of light in sequence.

[0061] The condenser lens 5 condenses divergent light that has passedthrough the rotating color filter 4 and directs it efficiently towardthe first lens array 6.

[0062] The first lens array 6 and the second lens array 7 are opticalintegrator elements. The first lens array 6 divides the beam condensedby the condenser lens 5 into small beams. The second lens array 7magnifies each of the small beams and superimposes them on the DMD 10.Thus, a uniform illumination beam is formed on the DMD 10 as an integralvalue of the small beams.

[0063]FIGS. 4A and 4B are a front view and a side view of the first lensarray 6, respectively. FIGS. 5A and 5B are a front view and a side viewof the second lens array 7, respectively. The first lens array 6includes a two-dimensional array of first lenses 6 a that areapproximately similar to the display area of the DMD 10. The second lensarray 7 includes a two-dimensional array of second lenses 7 a that arethe same as the first lenses 6 a in shape. Each of the second lenses 7 ais decentered appropriately so that the small beams that have passedthrough the corresponding first lenses 6 a are superimposed on the DMD10.

[0064] In this example, the second lenses 7 a of the second lens array 7have the same shape as that of the first lenses 6 a. However, the secondlenses are not limited thereto. For example, each of the first lenses 6a may be decentered, and the second lenses with different apertureshapes may be combined with the first lenses 6 a.

[0065] Alternatively, a lens with positive power may be located close tothe exit side of the second lens array 7 instead of decentering thesecond lenses 7 a, thus providing the superimposition effect.

[0066] The optical path of light emanating from the illumination system8 is bent by the reflection mirror 9, and then the light passes throughthe planoconvex lens 11 and enters the DMD 10.

[0067] The reflection mirror 9 is a plane mirror and is arranged so thatan optical axis 8 a of the illumination system 8 and an optical axis 12a of the projection lens 12 are skew lines. Moreover, the reflectionmirror 9 is arranged so that when viewed from the directionperpendicular to both optical axes 8 a, 12 a (i.e., the y-axisdirection) as shown in FIG. 1, an apparent point of intersection P ofthe optical axes 8 a, 12 a is located between the planoconvex lens 11and the projection lens 12.

[0068] The inclination angle of small mirrors on the DMD 10 is ±10degrees, and the reflection direction of incident light is controlled bychanging the inclination angle. This control is synchronized withrotation of the rotating color filter 4, and optical images of red,green, and blue are superimposed, so that a full color image can bedisplayed.

[0069] The maximum converging angle of illumination light is about 10degrees. The reflection mirror 9 is arranged so that the illuminationlight enters the plane of the DMD 10 at a bearing angle (an angle θbetween the incident light and the short side of the DMD 10 when viewedfrom the direction of a normal to the DMD 10, as shown in FIG. 2) of 45degrees and at an incident angle of 20 degrees.

[0070] The planoconvex lens 11 transmits both the incident light and theexit light of the DMD 10, is arranged so that a central axis (a normalpassing through the center of an effective portion of the DMD 10) 10 aof the DMD 10 and the optical axis 12 a of the projection lens 12 arecoaxial, and allows an exit pupil 8 b (the exit plane of the second lensarray 7 in FIG. 1) of the illumination system 8 to be conjugated with anentrance pupil 12 b of the projection lens 12.

[0071] The planoconvex lens 11 directs light that has passed through theexit pupil 8 b toward the DMD 10, and at the same time efficientlydirects the reflected light from the ON state of the DMD 10 toward theentrance pupil 12 b.

[0072] The projection lens 12 has an F number of 2.88 (the maximumconverging angle is 10 degrees), directs the reflected light in the ONstate of the DMD 10 toward a screen (not shown), and displays alarge-screen full color image on the screen.

[0073] In the projection display apparatus of this embodiment as shownin FIGS. 1 to 3, the power of the planoconvex lens 11 and an air gapbetween the planoconvex lens 11 and the projection lens 12 are setappropriately, so that the DMD 10 and the projection lens 12 can bearranged coaxially without using any expensive component such as a TIRprism.

[0074] Moreover, the optical axis 8 a of the illumination system 8 andthe optical axis 12 a of the projection lens 12 are skew lines. Thus, itis possible to eliminate mechanical contact or interference between theoptical components and utilize the space efficiently.

[0075] Further, the reflection mirror 9 is arranged appropriatelybetween the planoconvex lens 11 and the projection lens 12 so that whenviewed from the y-axis direction, the apparent point of intersection ofthe optical axis 8 a of the illumination system 8 and the optical axis12 a of the projection lens 12 is located between the planoconvex lens11 and the projection lens 12. Thus, it is possible to reduce the sizeof the apparatus.

[0076] The above configuration can provide an inexpensive compactprojection display apparatus that can achieve right projection by usinga reflection-type light modulator.

[0077] Embodiment 2

[0078]FIG. 6 shows the configuration of a projection display apparatusof Embodiment 2 of the present invention. When an xyz rectangularcoordinate system is defined as shown in the drawings, FIG. 6illustrates the configuration taken along the x-z plane. Similarly, FIG.7 illustrates the configuration taken along the y-z plane.

[0079] The basic operations from the light source 1 to the projectionlens 12 are the same as those in Embodiment 1, and therefore membershaving the identical function are denoted by the same reference numeralsand the explanation will not be repeated.

[0080] The distinct feature of this embodiment versus Embodiment 1 isthat the entrance pupil 12 b is eccentric with respect to the opticalaxis 12 a of the projection lens 12. In this embodiment, the entrancepupil 12 b is shifted in the direction of the minor axis (y-axis) of theDMD 10, as shown in FIG. 7. Therefore, when the inclination angle ofsmall mirrors on the DMD 10 is ±10 degrees, the maximum incident angleof illumination light is 10 degrees, and the illumination light entersthe plane of the DMD 10 at an incident angle of 24.5 degrees and abearing angle of 40 degrees.

[0081] The projection lens 12 has an F number of 2.0 (the maximumconverging angle is 14.5 degrees), and the entrance pupil 12 b has aneffective F number of 2.85.

[0082] The projection lens 12 contains a lens stop with a similar shapeto the entrance pupil 12 b and has a focus adjusting mechanism that canmove only along the optical axis 12 a of the projection lens 12 withoutrotating around the optical axis 12 a due to the eccentricity of theentrance pupil 12 b.

[0083] The entrance pupil 12 b may be shifted in the direction in whichthe angle between incident light and exit light of the DMD 10 becomeslarger. This increases the separation angle between the illuminationlight traveling from the reflection mirror 9 to the planoconvex lens 11and the projection light traveling from the planoconvex lens 11 to theprojection lens 12. Therefore, reflection mirror 9 can be located closerto the planoconvex lens 11. Consequently, an air gap between theplanoconvex lens 11 and the projection lens 12 can be reduced, and thusthe size of the apparatus also can be reduced.

[0084] The maximum converging angle required for the projection lens 12as well as the separation angle between the illumination light and theprojection light increase with the amount of eccentricity of theentrance pupil 12 b. Therefore, a projection lens having a small Fnumber is necessary. It is desirable that the amount of eccentricity isset appropriately in view of the set size, the F number of a projectionlens, or the like.

[0085] This embodiment shows an example in which the bearing angle ofthe illumination light is 40 degrees, and the entrance pupil 12 b isshifted in the direction of the minor axis (y-axis) of the DMD 10.Although the present invention is not limited thereto, it is preferableto set the bearing angle of the illumination light between the directionof inclination of the small mirrors on the DMD 10 (i.e., in thisembodiment, the direction that tilts 45 degrees from the minor axis(y-axis) of the DMD 10) and the minor axis (y-axis) of the DMD 10.

[0086] In the projection display apparatus of this embodiment as shownin FIGS. 6 and 7, the power of the planoconvex lens 11 and an air gapbetween the planoconvex lens 11 and the projection lens 12 are setappropriately, so that the DMD 10 and the projection lens 12 can bearranged coaxially without using any expensive component such as a TIRprism.

[0087] Moreover, the optical axis 8 a of the illumination system 8 andthe optical axis 12 a of the projection lens 12 are skew lines. Thus, itis possible to eliminate mechanical contact or interference between theoptical components and utilize the space efficiently.

[0088] Further, the reflection mirror 9 is arranged appropriatelybetween the planoconvex lens 11 and the projection lens 12 so that whenviewed from the y-axis direction, the apparent point of intersection Pof the optical axis 8 a of the illumination system 8 and the opticalaxis 12 a of the projection lens 12 is located between the planoconvexlens 11 and the projection lens 12. Thus, it is possible to reduce thesize of the apparatus.

[0089] Further, appropriate eccentricity of the entrance pupil 12 b canreduce a gap between the planoconvex lens 11 and the projection lens 12.

[0090] The above configuration can provide an inexpensive projectiondisplay apparatus that is more compact than the apparatus in Embodiment1 and can achieve right projection by using a reflection-type lightmodulator.

[0091] Embodiment 3

[0092]FIG. 8A shows the configuration of a projection display apparatusof Embodiment 3 of the present invention. When an xyz rectangularcoordinate system is defined as shown in the drawings, FIG. 8Aillustrates the configuration taken along the x-z plane. Similarly, FIG.9 illustrates the configuration taken along the y-z plane.

[0093]FIG. 8B is a front view of the DMD 10 when viewed from thedirection of the arrow on the line 8B-8B in FIG. 8A.

[0094] The basic operations from the light source 1 to the projectionlens 12 are the same as those in Embodiments 1 and 2, and thereforemembers having the identical function are denoted by the same referencenumerals and the explanation will not be repeated.

[0095] Like Embodiment 2, this embodiment allows the entrance pupil 12 bto be shifted in the direction of the minor axis (y-axis) of the DMD 10,as shown in FIG. 9.

[0096] The distinct feature of this embodiment versus Embodiment 1 isthat the entrance pupil 12 b is eccentric with respect to the opticalaxis 12 a of the projection lens 12, and at the same time a convergingangle in the eccentric direction of the entrance pupil 12 b is smallerthan a converging angle in the direction perpendicular to the eccentricdirection.

[0097]FIGS. 10A and 10B are schematic diagrams, each showing therelationship between the range of a maximum converging angle and theentrance pupil of the projection lens 12. FIG. 10A shows an entrancepupil 101 and a range 102 of the maximum converging angle required forthe projection lens 12 when a converging angle in the eccentricdirection 100 (y-axis direction) is the same as a converging angle inthe direction (x-axis direction) perpendicular to the eccentricdirection (corresponding to Embodiment 2). FIG. 10B shows an entrancepupil 103 and a range 104 of the maximum converging angle required forthe projection lens 12 when a converging angle in the eccentricdirection 100 (y-axis direction) is smaller than a converging angle inthe direction (x-axis direction) perpendicular to the eccentricdirection (corresponding to Embodiment 3). In either case, the amount ofeccentricity and the area of the entrance pupil (the effective F number,indicated by the diagonally shaded portion) are the same.

[0098] In the entrance pupil 103, F_(V) represents a maximum length inthe eccentric direction 100 (y-axis direction), and F_(H) represents amaximum length in the direction (x-axis direction) perpendicular to theeccentric direction.

[0099] As can be seen from the comparison of FIGS. 10A and 10B, when theeccentric entrance pupils have the same effective F number, the range ofa maximum converging angle of the projection lens can be reduced more bymaking a converging angle in the eccentric direction 100 smaller than aconverging angle in the direction perpendicular to the eccentricdirection. In other words, the same performance can be achieved with aprojection lens having a small maximum converging angle (i.e., a large Fnumber).

[0100] Moreover, a smaller converging angle in the eccentric direction100 leads to a decrease in interference between the illumination lighttraveling from the reflection mirror 9 to the planoconvex lens 11 andthe projection light traveling from the planoconvex lens 11 to theprojection lens 12. Therefore, the reflection mirror 9 can be locatedcloser to the planoconvex lens 11. Consequently, an air gap between theplanoconvex lens 11 and the projection lens 12 can be reduced.

[0101] To obtain an exit pupil 8 b of the illumination system 8 thatmatches with the entrance pupil 12 b, e.g., a first lens array 86 havinga shape as shown in FIGS. 11A, 11B and a second lens array 87 having ashape as shown in FIGS. 12A, 12B may be used.

[0102]FIG. 11A is a front view of the first lens array 86, and FIG. 11Bis a cross-sectional view taken along the line 11B-11B in FIG. 11A. Eachof first lenses 86 a of the first lens array 86 is decentered so thatbeams that have passed through the first lenses 86 a are focused on thecorresponding second lenses 87 a of the second lens array 87.

[0103]FIG. 12A is a front view of the second lens array 87, and FIG. 12Bis a cross-sectional view taken along the line 12B-12B in FIG. 12A. Eachof the second lenses 87 a of the second lens array 87 is decenteredappropriately so that the beams that have passed through thecorresponding first lenses 86 a are superimposed on the DMD 90.

[0104] The second lens array 87 may be set so that the direction of theminor axis 87 b substantially coincides with the eccentric direction ofthe entrance pupil 12 b, and the dimensions in the respective directionsof the minor axis 87 b and the major axis 87 c match with the convergingangles of the projection lens 12 in the corresponding directions.

[0105] The suitable effects of the present invention may be obtained bysatisfying the following formulas (1) and (2):

0.5×L _(DMD) ≦D ₁ ≦L _(DMD)  (1)

0.3f≦D ₂ ≦f  (2)

[0106] where L_(DMD) represents a diagonal length (FIG. 8B) of aneffective display area of the DMD 10, D₁ represents an air gap betweenthe DMD 10 and the planoconvex lens 11, D₂ represents an air gap betweenthe planoconvex lens 11 and the projection lens 12, and f represents afocal length of the planoconvex lens 91.

[0107] For the formula (1), when D₁ is less than the lower limit,unwanted reflected light that occurs between the DMD 10 and theplanoconvex lens 11 is increased and adversely affects the imagequality. When D₁ is more than the upper limit, an effective diameter ofthe planoconvex lens 11 is increased, so that the size of the apparatusis increased.

[0108] For the formula (2), when D₂ is less than the lower limit, itbecomes difficult to arrange the reflection mirror 9. When D₂ is morethan the upper limit, a back focal length of the projection lens 12 isincreased, causing problems such that aberration is not correctedeasily, and the size of the apparatus is increased.

[0109] In both Embodiment 1 (FIGS. 1 to 3) and Embodiment 2 (FIGS. 6 and7), the suitable effects also can be obtained by satisfying the aboveformulas (1) and (2).

[0110] It is further preferable to satisfy the following formulas (3)and (4):

2×θ_(DMD)≦θ_(i)≦2.5×θ_(DMD)  (3)

0.35≦F _(V) /F _(H)≦0.95  (4)

[0111] where θ_(DMD) represents the inclination angle of small mirrorson the DMD 10, θ_(i) represents the incident angle of illumination light(corresponding to the optical axis 8 a of the illumination system 8 inthis embodiment) with respect to the central axis 10 a of the DMD 10,F_(V) represents the maximum length of the entrance pupil 12 b in theeccentric direction, and F_(H) represents the maximum length of theentrance pupil 12 b in the direction perpendicular to the eccentricdirection.

[0112] For the formula (3), when θ_(i) is less than the lower limit, theseparation angle between incident light and exit light of the DMD 10becomes smaller, making it difficult to arrange the reflection mirror 9.When θ_(i) is more than the upper limit, the maximum converging anglerequired for the projection lens 12 becomes larger, thus increasing thesize of the projection lens 12.

[0113] For the formula (4), when F_(V)/F_(H) is less than the lowerlimit, the entrance pupil area (where a light beam passes through) isreduced relatively in the range of a maximum converging angle of theprojection lens 12, so that a wasted region is increased. WhenF_(V)/F_(H) is more than the upper limit, the maximum converging anglerequired for the projection lens 12 becomes larger, thus increasing thesize of the projection lens 12.

[0114] In Embodiment 2 as shown in FIGS. 6 and 7, the suitable effectsalso can be obtained by satisfying the above formula (3).

[0115] In the configuration as shown in FIGS. 8A and 8B, L_(DMD)=20.3mm, D₁=10 mm, D₂=40 mm, f=100 mm, θ_(DMD)=10 degrees, θ_(i)=24 degrees,and F_(V)/F_(H)=0.7. Each of the mirrors on the DMD 10 is inclined inthe direction at 45 degrees with respect to the minor axis (y-axis). Theillumination light enters the DMD 10 at a bearing angle of 40 degreesmeasured from the minor axis of the DMD 10.

[0116] The F number of the projection lens 12 is 2.1. The projectionlens 12 contains a lens stop with similar shape to the entrance pupil 12b and has a focus adjusting mechanism that can move only along theoptical axis 12 a of the projection lens 12 without rotating around theoptical axis 12 a due to the eccentricity of the entrance pupil 12 b.

[0117] It is preferable to set the eccentric direction of the entrancepupil 12 b so that the bearing angle of the illumination light isbetween the direction of the minor axis of the DMD 10 and the directionof inclination of the small mirrors.

[0118] In the projection display apparatus of this embodiment as shownin FIGS. 8A, 8B, and 9, the power of the planoconvex lens 11 and an airgap between the planoconvex lens 11 and the projection lens 12 are setappropriately, so that the DMD 10 and the projection lens 12 can bearranged coaxially without using any expensive component such as a TIRprism.

[0119] Moreover, the optical axis 8 a of the illumination system 8 andthe optical axis 12 a of the projection lens 12 are skew lines. Thus, itis possible to eliminate mechanical contact or interference between theoptical components and utilize the space efficiently.

[0120] Further, the reflection mirror 9 is arranged appropriatelybetween the planoconvex lens 11 and the projection lens 12 so that whenviewed from the y-axis direction, the apparent point of intersection Pof the optical axis 8 a of the illumination system 8 and the opticalaxis 12 a of the projection lens 12 is located between the planoconvexlens 11 and the projection lens 12. Thus, it is possible to reduce thesize of the apparatus.

[0121] Further, the entrance pupil 12 b is eccentric appropriately, anda converging angle in the eccentric direction is smaller than aconverging angle in the direction perpendicular to the eccentricdirection, so that the projection lens 12 having a small convergingangle (i.e., a large F number) can be used. At the same time, an air gapbetween the planoconvex lens 11 and the projection lens 12 also can bereduced.

[0122] The above configuration can provide an inexpensive projectiondisplay apparatus that is more compact than the apparatuses inEmbodiments 1 and 2 and can achieve right projection by using areflection-type light modulator.

[0123] Embodiment 4

[0124]FIG. 13 shows the configuration of a projection display apparatusof Embodiment 4 of the present invention. Reference numeral 131 denotesa first cabinet, 132 denotes a second cabinet, 133 denotes a thirdcabinet, and 134 denotes a coupling member. The basic operations fromthe light source 1 to the projection lens 12 are the same as those inEmbodiment 3, and therefore members having the identical function aredenoted by the same reference numerals and the explanation will not berepeated.

[0125] The first cabinet 131 holds the illumination system 8 andincludes an entrance window 131 a through which emitted light of thelamp 1 enters and an exit window 131 b through which illumination lightemanates.

[0126] The second cabinet 132 holds the reflection mirror 9, the DMD 10,the planoconvex lens 11, and the projection lens 12 and includes anentrance window 132 a through which the illumination light enters.

[0127] The third cabinet 133 holds the lamp 1, the concave mirror 2, andthe UV-IR cut filter 3 and includes an exit window 133 a through whichthe emitted light of the lamp 81 emanates.

[0128] The coupling member 134 couples the exit window 131 b of thefirst cabinet 131 to the entrance window 132 a of the second cabinet 132so that the optical axes 8 a of the illumination light substantiallycoincide. The coupling member 134 includes a three-directional (x, y,and z) adjusting mechanism.

[0129] A coupling member 135 couples the exit window 133 a of the thirdcabinet 133 to the entrance window 131 a of the first cabinet 131 sothat the optical axis la of the lamp 81 and the optical axis 8 a of theillumination light substantially coincide. The coupling member 135includes a three-directional (x, y, and z) adjusting mechanism.

[0130] A projection optical system generally requires higher accuracy ofcomponents than an illumination optical system does. The projectiondisplay apparatus in FIG. 13 allows the light source, the illuminationoptical system, and the projection optical system to be held indifferent cabinets. Therefore, this apparatus has the advantage ofselecting appropriate processing accuracy or materials for each of thecabinets. For example, materials and processing methods may be appliedwith an emphasis on cost for the first cabinet 131, accuracy for thesecond cabinet 132, and heat resistance for the third cabinet 133.

[0131] Moreover, the optical components are divided into the cabinets toform units, thereby facilitating maintenance.

[0132] The coupling members 134, 135 include an adjusting mechanism, sothat the adjusting mechanism of each optical component, which has beenneeded for a conventional apparatus, can be removed.

[0133] This embodiment shows an example in which the projection displayapparatus is divided into three cabinets. However, the first cabinet 131and the third cabinet 133 may be formed as a common cabinet.

[0134] The above configuration can provide an inexpensive projectiondisplay apparatus that can facilitate the maintenance of opticalcomponents.

[0135]FIG. 13 shows the projection display apparatus provided with theoptical system of Embodiment 3. However, the present invention is notlimited thereto, and the projection display apparatus may include, e.g.,the optical system of Embodiment 1 or 2.

[0136] Embodiment 5

[0137]FIG. 14A is a perspective front view of a rear-projection displayapparatus of Embodiment 5 of the present invention, and FIG. 14B is aperspective side view of the apparatus. Reference numeral 141 is aprojection display apparatus, 142 is a transmission-type screen, and 143is a cabinet. The transmission-type screen 142 is held by the cabinet143, in which the projection display apparatus 141 according toEmbodiment 4 is arranged.

[0138] Light emanating from the projection lens of the projectiondisplay apparatus 141 is reflected by a reflection mirror 144 and entersthe transmission-type screen 142.

[0139] The transmission-type screen 142 is formed, e.g., of a Fresnellens and a lenticular lens. The focal length of the Fresnel lens issubstantially equal to the optical path length from the Fresnel lens tothe projection lens, and incident light is refracted appropriately andtransmitted toward the front of the screen 142. The viewer can observean image that is magnified and projected by the projection displayapparatus 141 through the transmission-type screen 142.

[0140] Using the projection display apparatus 141 of the presentinvention eliminates the need for offset of the Fresnel lens, so that alarge-screen image with high quality and high uniformity in resolutionor brightness can be achieved. Moreover, the whole cabinet can be madecompact because the apparatus is small.

[0141] The above configuration can provide an inexpensive compactrear-projection display apparatus that can perform high-quality imagedisplay by using a reflection-type light modulator.

[0142] Embodiment 6

[0143]FIG. 15 is a perspective view of a rear-projection displayapparatus of Embodiment 6 of the present invention. Reference numeral151 is a projection display apparatus, 152 is a transmission-typescreen, and 153 is a cabinet. Four transmission-type screens 152 areheld by the cabinet 153, in which the same number of projection displayapparatuses according to Embodiment 4 are arranged in one-to-onecorrespondence with the screens 152.

[0144] When images of the projection display apparatuses 151 arearranged to display a multi-screen, it is preferable to reduce adifference in brightness or resolution between the screens located onboth sides of the boundary of each screen.

[0145] In this embodiment, using the projection display apparatuses 151of the present invention eliminates the need for offset of a Fresnellens, so that display images in each of the screens have resolution orbrightness performance that is rotationally symmetrical with respect tothe screen center. Therefore, when these images are arranged to form amulti-screen, a difference in brightness or resolution between thescreens located on both sides of the boundary of each screen can be madeextremely small except for variations in the individual screens.

[0146] The above configuration can provide a rear-projection displayapparatus that can achieve high image quality, a small difference inimage quality between the screens, and multi-screen display by using aplurality of projection display apparatuses, each of which includes areflection-type light modulator.

[0147] In FIGS. 14A, 14B and 15, any of the projection displayapparatuses according to Embodiments 1 to 4 may be used as theprojection display apparatuses 141, 151, and in either case the sameeffect can be obtained.

[0148] A field stop for cutting off unwanted light may be provided atthe aperture on the exit side of the projection lens. This makes itpossible to achieve a high-contrast display image.

[0149] In Embodiments 1 to 4, two lens arrays are used in theillumination system 8. However, an optical integrator element such as aglass rod also may be used. A condenser lens also may be used to produceillumination light instead of the optical integrator element.

[0150] In Embodiments 1 to 4, the plane mirror 9 is used as a reflectionsystem. However, a curved mirror (e.g., spherical, aspherical, free-formsurface, or parabolic) may be used as well.

[0151] In Embodiments 1 to 4, the DMD 10 is used as a reflection-typelight modulator. However, any component may be used as long as it canspatially modulate incident light by causing a change in the incidentlight such as polarization or diffraction.

[0152] In Embodiments 1 to 4, the planoconvex lens 11 is used as a lenselement. However, the convex surface of a lens is not limited to theorientation as described in the embodiments. Also, for example, adouble-convex lens or gradient index lens may be used instead of theplanoconvex lens.

[0153] The invention may be embodied in other forms without departingfrom the spirit or essential characteristics thereof. The embodimentsdisclosed in this application are to be considered in all respects asillustrative and not limiting. The scope of the invention is indicatedby the appended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are intended to be embraced therein.

1. A projection display apparatus comprising: a light source; anillumination system for condensing light emitted from the light sourceinto illumination light; a reflection system for bending an optical pathof the illumination light; a reflection-type light modulator that isilluminated with the illumination light bent by the reflection systemand forms an optical image in accordance with an image signal; aprojection system for projecting the optical image formed on thereflection-type light modulator; and a lens element arranged on opticalpaths of incident light and exit light of the reflection-type lightmodulator, wherein an optical axis of the illumination system and anoptical axis of the projection system are skew lines, and the lenselement allows an exit pupil of the illumination system to be conjugatedsubstantially with an entrance pupil of the projection system.
 2. Theprojection display apparatus according to claim 1, wherein the entrancepupil is eccentric with respect to the optical axis of the projectionsystem.
 3. The projection display apparatus according to claim 2,wherein a converging angle in the eccentric direction of the projectionsystem is smaller than a converging angle in a direction perpendicularto the eccentric direction.
 4. The projection display apparatusaccording to claim 2, wherein the projection system comprises a focusadjusting mechanism that does not rotate around the optical axis of theprojection system.
 5. The projection display apparatus according toclaim 1, wherein when viewed from a direction perpendicular to both theoptical axis of the illumination system and the optical axis of theprojection system, an apparent point of intersection of the optical axisof the illumination system and the optical axis of the projection systemis located between the lens element and the projection system.
 6. Theprojection display apparatus according to claim 1, wherein the opticalaxis of the reflection-type light modulator coincides with the opticalaxis of the projection system.
 7. The projection display apparatusaccording to claim 1, further comprising a first cabinet and a secondcabinet, wherein the first cabinet holds the illumination system andcomprises an exit window through which light emanating from theillumination system passes, the second cabinet holds the reflectionsystem, the reflection-type light modulator, the lens element, and theprojection system and comprises an entrance window through which lightfrom the illumination system enters, and the exit window and theentrance window are coupled together.
 8. The projection displayapparatus according to claim 7, further comprising a coupling memberbetween the exit window and the entrance window, wherein the couplingmember comprises an adjusting mechanism for adjusting an optical axis oroptical path length.
 9. The projection display apparatus according toclaim 1, wherein the illumination system comprises an optical integratorelement.
 10. The projection display apparatus according to claim 9,wherein the optical integrator element comprises two lens array plates,and each of a plurality of lenses that constitute at least the lensarray plate located closer to the light source is decenteredappropriately.
 11. A rear-projection display apparatus comprising: theprojection display apparatus according to claim 1; a transmission-typescreen for displaying an image projected by the projection displayapparatus; and a cabinet for housing the projection display apparatusand holding the transmission-type screen.
 12. A rear-projection displayapparatus comprising: a plurality of projection display apparatusesaccording to claim 1; transmission-type screens for displaying imagesprojected by the projection display apparatuses; and a cabinet forhousing the projection display apparatuses and holding thetransmission-type screens.
 13. The rear-projection display apparatusaccording to claim 11 [[or 12]], wherein the projection displayapparatus comprises a field stop on the transmission-type screen side.14. The rear-projection display apparatus according to claim 12, whereinthe projection display apparatus comprises a field stop on thetransmission-type screen side.